Re: when to introduce solids
welcome! the American Academy of Pediatrics recommends not starting solids until 6 months. advice to start at 4 months is out of date. developmental signs of readiness include: sitting up unassisted, pincer grasp (so baby can get food to her mouth independently), has lost the tongue-push reflex, and i think i'm missing 1 more. most babies get those right around 6 months; it would be highly unusual for yours to have them all at 4.5 months, but it is possible. showing signs of interest is NOT a sign that baby is developmentally ready for solids - they just want to know what we're doing and imitate! an empty spoon/plate/cup will satisfy that.
there are good reasons to wait as long as possible: there is some evidence that early solids contributes to autoimmune problems (like eczema, allergies, ibs, etc) and breastmilk poo is SOOO much less gross than solids poo.
Nursing, pumping, cloth-diapering, babywearing, working professor mama with the awesomest SAHD ever.